Procedures such as balloon angioplasty and numerous other medical procedures such as atherectomy and laser angioplasty occur in catheterization labs (cath labs). In such labs, a physician will direct a catheter through vessels remote from a patient's heart using real-time fluoroscopic and static X-ray images. The static X-ray image is conventionally referred to as the "roadmap" because it is an image of the coronary arteries stained with radio-opaque dies. The physician uses this image in maneuvering the catheter towards the desired coronary artery, hence its name of "roadmap." As the physician remotely guides the catheter towards coronary arteries, he or she can compare the progress of the catheter as shown on the fluoroscopic image with the location of the coronary arteries as revealed on the roadmap image.
In addition to the fluoroscopic and roadmap images, the physician may also view intravascular ultrasound images gathered from a rotating transducer associated with the catheter. Using ultrasound, the physician may directly image plaque affecting coronary arteries before treatment with, for example, balloon angioplasty. In ordinary operation, the fluoroscopic, roadmap and ultrasound images are viewed on their respective monitors. Each image can have a different brightness, color, etc. The differences in the images may strain a physician's eyes when comparing images on differing monitors. The differences in image quality from monitor to monitor may also increase the difficulty of pinpointing regions of interest because the human eye is likely to focus on the noticeable difference in image quality rather than clinically important image details. Often, therefore, a physician will want the roadmap or the fluoroscopic images to be imported and displayed in a window on the ultrasound monitor or vice versa. The importation of video signals from cath lab fluoroscopic or X-ray monitors onto an ultrasound monitor is complicated by the widely divergent video standards employed by the various manufacturers of such equipment. Moreover, fluoroscopic and X-ray monitors may often have grounds which may float at voltages considerably above the true ground. Such voltages represent a danger to patients in contact with an ultrasound system which is displaying imported video signals from monitors with such floating grounds. Thus, isolation from such potential danger is required in an ultrasound system capable of displaying imported X-ray video signals.
Prior art systems which allowed the importation of X-ray video signals for display on an intravascular ultrasound monitor were cumbersome. Such systems required hardware adapted for the video signals generated by the equipment in a particular cath lab. Should the system be moved to a cath lab using different X-ray equipment, a corresponding change in the hardware was required to accommodate the changed video signals. Consider the following table which illustrates the many different video standards for a number of major manufacturers of cath lab imaging monitors.
TABLE 1 __________________________________________________________________________ X-Ray Image Standards Table For reference only RS-170
Siemens Seimens GE GE Phillips Shimadu Standard 525/60 625/50 1023/60 1249/50 1023/60 1249/50 1049/60 1125/60 1023/120 __________________________________________________________________________ H Drive 6.4 .mu.s 6.4 .mu.s 2.5 .mu.s 2.5 .mu.s 4.58 .mu.s 4.5 .mu.s 3.17 .mu.s 2.96 .mu.s H Front porch 1.6 .mu.s 1.6 .mu.s 0.8 .mu.s 0.8 .mu.s 0.79 .mu.s 0.21 .mu.s H Blank 11 .mu.s 11.2 .mu.s 7.1 .mu.s 6 .mu.s 7.12 .mu.s 7.01 .mu.s 5.55 .mu.s 7.58 .mu.s H Sync 4.8 .mu.s 4.8 .mu.s 2.5 .mu.s 2.5 .mu.s 3.05 .mu.s 3 .mu.s 2.38 .mu.s 2.07 .mu.s H Freq 15750 Hz 15625 Hz 30.69 KHz 31.22 KHz 30.69 KHz 31.22 KHz 31.47 KHz 33.74 KHz 63 KHz H Key 1.2 .mu.s 1.2 .mu.s H Line Duration 63.5 .mu.s 64 .mu.s 32.58 .mu.s 32.03 .mu.s 32.58 .mu.s 32.03 .mu.s 31.77 .mu.s 29.63 .mu.s V Freq 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz 60 Hz 120 Hz V Drive 10.5 H 12.5 H 20 H 20 H 20.5 H 20.5 H 20.5 H 22.5 H V Front Porch 3 H 2.5 H 3 H 3 H 3 H 3 H 3 H 5.5 H V Sync 3 H 2.5 H 3 H 3 H 3 H 3 H 3 H 5 H Equalizer 2.35 .mu.s 2.4 .mu.s 1 .mu.s 1 .mu.s 1.53 .mu.s 1.5 .mu.s 1.2 .mu.s 1.12 .mu.s Equalizer Pulses 6 5 6 6 6 6 6 11 Serration Pulse 4.5 .mu.s 4.8 .mu.s 1.8 .mu.s 1.8 .mu.s 2.03 .mu.s 2 .mu.s 2.38 2.07 Serration Pulses 6 5 6 6 6 6 6 10 Field Duration 16.7 ms 20 ms 16.7 ms 20 ms 16.7 ms 20 ms 16.7 ms 16.7 ms Aspect Ratio 4:3 4:3 1:1 1:1 1.1:1 1.1:1 1:1 5:4 __________________________________________________________________________
Given the plethora of video standards encountered in any given catheterization lab, there is a need in the art for a system which can accommodate such a wide variety of video standards. Such a system lowers health care costs because specialized video conversion systems need not be developed. Instead, the use of the present invention allows a single system to be universally used, regardless of the X-ray video equipment in a particular cath lab.